US5600317A - Apparatus for the conversion of analog audio signals to a digital data stream - Google Patents
Apparatus for the conversion of analog audio signals to a digital data stream Download PDFInfo
- Publication number
- US5600317A US5600317A US08/490,136 US49013695A US5600317A US 5600317 A US5600317 A US 5600317A US 49013695 A US49013695 A US 49013695A US 5600317 A US5600317 A US 5600317A
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- United States
- Prior art keywords
- data stream
- circuit
- signal
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/10—Calibration or testing
- H03M1/1009—Calibration
- H03M1/1028—Calibration at two points of the transfer characteristic, i.e. by adjusting two reference values, e.g. offset and gain error
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/12—Analogue/digital converters
- H03M1/18—Automatic control for modifying the range of signals the converter can handle, e.g. gain ranging
- H03M1/188—Multi-path, i.e. having a separate analogue/digital converter for each possible range
Definitions
- the invention relates to an apparatus for the conversion of analog audio signals to a digital data stream.
- A/D converters In order to widen the dynamic range of analog/digital converters (A/D converters) that are available in audio technology, a converter is used by means of the so-called "gain-ranging" technique in each of two parallel signal paths, the one serving for high levels and the other for low levels of the audio signal that is to be converted.
- the audio signal to be converted is amplified analogically in one path before conversion, and amplified in the other path by the same amount, but digitally after the A/D conversion. Both paths terminate in a double-throw switch which prepares for further processing the digital data stream from whichever path is optimally modulated by the audio signal that is to be converted.
- Apparatus of this technology generally have the disadvantage that the switching from one path to the other for the processing of the digital data stream can make undesired clicks, distortion and noise modulation audible. Above all, circuit noise, DC offsets and gain errors in the circuits largely nullify the advantage of the dynamic gain. Attempts are made to minimize these disturbances by suppressing their subjective audibility.
- a soft smoothing over in the switching from one path to the other has the considerable disadvantage that the data streams have to be delayed by the amount of the smoothing time, which in most cases is not acceptable.
- the invention therefore is addressed to the problem of improving the high-resolution conversion of analog audio signals to a digital data stream at low cost, and especially of reducing those disturbances which occur upon switching from one signal path to another signal path, for the preparation of a digital data stream very accurately corresponding to the audio signal received.
- a circuit for the conversion of an analog audio signal to a bit stream of high resolution in which the audio signal is converted on a plurality of parallel paths of different amplitude sensitivity, and then the errors due to conversion are compensated. Due to the compensation of errors between conversion and switching, in the latter the errors caused in conversion can no longer occur, so that the disturbances are eliminated. To further minimize disturbances it is recommendable to operate the switching of the prepared data stream from either of the two paths in accordance with the amplitude of the audio signal to be converted. Additional preferred embodiments of the invention are given in the subordinate claims.
- FIG. 1 is a circuit diagram of an embodiment of the invention.
- the apparatus consists of two signal paths 1 and 2, as well as a control path 3, which are connected in parallel between an input terminal 4 marked Urn and a double-throw switch 5.
- the first signal path 1 has three stages in tandem, the first stage 21 of which contains, connected in series, an amplifier 22 with the amplification factor V, a voltage limiter 24 and an A/D converter 26.
- the input line 23 of the amplifier 22 is connected to the signal input 4.
- the output line 25 from the A/D converter 26 is simultaneously the input signal line for the second stage 28.
- the output line 61 of the subtractor 62 is both the signal output line of the second stage 28 and the signal input line for the third stage 66 of the first signal path 1.
- a branch 49 of the signal line 61 leads to an x-input of a gain error detector 44 from the third stage 13 of the second signal path 2.
- Another branch line 63 of the signal line 61 leads to an input of the envelope emcee generator 68 whose output line 65 leads into a multiplier 70.
- the multiplier 70 receives another input from a noise generator 72.
- the output of the multiplier 70 leads through line 71 to an input of an adder 74 which receives its other input from the signal line 61.
- the output line 77 of the adder leads to a switch contact 54 of the double-throw switch 5.
- the second signal path 2 likewise has three stages 11, 12 and 13 in series, the first stage 11 of which has an A/D converter connected at the input end to the terminal 4. At the output end the A/D converter 14 is connected to the input of the second stage 12 through line 15.
- the input line 15 of the second stage 12 leads on the one hand to the input of a subtractor 16 and through a branch line to the charging input of an offset register 18 which, when a CAL control signal is present on control signal line 31 at the control input of the offset register 18, is charged by the signals arriving on line 15.
- the output line 61 of the subtractor 62 is both the signal output line of the second stage 28 and the signal input line for the third stage 66 of the first signal path 1.
- a branch 49 of the signal line 61 leads to an x-input of a gain-error detector 44 from the third stage 13 of the second signal path 2.
- Another branch 63 of the signal line 61 leads to an input of an envelope curve generator 68 whose output line 65 leads into a multiplier 70.
- the multiplier 70 receives an additional input from a noise generator 72.
- the output of the multiplier 70 leads through line 71 to an input of an adder 74 which receives its other input from the signal line 61.
- the output line 77 of the adder runs to a switch contact 54 of the double-throw switch 5.
- the second signal path 2 likewise has three stages 11, 12 and 13 in series, the first stage 11 of which has an A/D converter 14 connected to the terminal 4 at the input end. At the output end the A/D converter 14 is connected to the input of the second stage 12 through line 15.
- Line 15 of the second stage 12 leads on the one hand to the input of a subtractor 16 and via a branch line to the charging input of an offset register 18 which, when a CAL control signal is present on control signal line 31 at the control input of the offset register 18, is charged with the signals arriving on line 15.
- the content of the offset register 18 passes through line 17 into the subtractor 16.
- the output line 19 from the subtractor 16 is at the same time the output line of the second stage 12 and the input line for the third stage 13.
- the third stage 13 has a multiplier 42 which receives the signals arriving on signal line 19.
- a branch 41 of the signal line 19 goes to a y-input of the gain-error detector 44 which can charge a coefficient register 46 through an output line 43.
- the digital value contained in the coefficient register 46 can be fed through output line 45 as an additional input to the multiplier 42.
- the output line 47 of the multiplier 42 leads to an additional contact 52 of the double-throw switch 5.
- Control path 3 contains a series circuit composed of a full-wave rectifier 32 whose input is connected to the signal input 4, a Schmitt trigger 34 and a re-triggerable monostable multivibrator 36 whose control signal output line 33 runs on the one hand to a control input of the double-throw switch 5 and on the other hand via branch line 35 to an additional input of the envelope curve generator 68.
- a control signal on line 33 causes the arm 56 of double-throw switch 5 to change from contact 52 to contact 54 or vice-versa.
- the selected digital data stream is made available by arm 56 through terminal 58 for further processing.
- the externally formed calibration signal is present at terminal 38 as the CAL control signal which is fed via signal line 31, as mentioned, to the offset registers 18 and 64 and also via control signal line 37 to the control connection of a relay 80.
- the relay 80 can short-circuit the signal input terminal 4 to ground in accordance with the presence of a control signal on line 37.
- double-throw switch 5 is an electronic switch which here is represented and described as a double-throw switch only for simplification.
- the A/D converters 14 and 26 and the circuits of the second and third stages 12 an 13, and 28 and 66 are cycled by a cycling source not shown, which provides a sampling cycle.
- the corresponding sampling signal lines have been omitted from the drawing for the sake of clarity.
- the two stages 12 and 28 are of equal construction and they serve to compensate for erroneous direct-current shifts occurring in the corresponding first stages 11 and 21.
- the calibration signal CAL at terminal 38 serves for this purpose.
- the calibration can be performed at any desired time. It is recommendable to perform the calibration prior to the audio signal conversion, as well as at later points of time if necessary. Since the DC shift as a rule changes but slowly, it is sufficient to produce the calibration only at relatively long time intervals.
- the CAL signal furthermore opens tile inputs to the offset registers 18 and 64 so that upon the next sampling pulse they pick up the data word representing the offset error and cause this data word to be subtracted from the input signal from converters 14 and 26 in the subtractors 16 and 62, respectively. Therefore data words with a zero content will be present on the output lines 19 and 61.
- the offset registers 18 and 64 contain the value newly loaded during the calibration, so that the amount of correction contained in the offset registers is constantly subtracted from the data streams delivered from the A/D converters 14 and 26. Thus the offset error in both data streams is compensated out of stages 1 and 2.
- the signal path 1 serves for the A/D conversion of low-level audio signals U In
- signal path 2 is used for the A/D conversion of the high-level audio signals U In
- the control signal path 3 it is determined whether the level of the input voltage U In has exceeded a threshold determined by the setting of the Schmitt trigger 34. If the level of U In remains below the threshold value, the monostable multivibrator 36 is not triggered, so that the digital data stream present at the output contact 58 is taken out of the signal path 1.
- the threshold value is determined by the dimensions of the Schmitt trigger which operates when the amplitude of U In rises, just before the end of the contents of the A/D converter.
- the action of the Schmitt trigger 34 produces a triggering of the next-following monostable multivibrator 36, which in turn produces on the control signal line a signal which causes the switch 5 to change the arm over to contact 52, so that the digital data stream that has been prepared at contact 58 is taken out of the signal path 2.
- the A/D converter 14 (in contrast to A/D converter 26) obtains the signal unamplified, its stock of values still permits coding of the audio input signal at levels that are already above the modulation limit of the A/D converter 26 and thus above the threshold.
- the data stream leaving the A/D converter 14 is amplified in the next-following multiplier 42 by the coefficients contained in the coefficient register 46, at first by an amplification V that is equal to the amplification V of the amplifier 22.
- x i /y i is a data word from the signal path 1
- y i is a data word from signal path 2 amplified by the factor V
- I . . . n is the number of sampling pulses.
- the values from line 41 are amplified by the factor V before the averaging is done, and the above-mentioned average that has been determined is also multiplied by the amplification factor V, so as to assure the said amplification of the data stream leaving stage 12 in the multiplier 42.
- the gain error detector 44 performs the said averaging increased by the factor V only for input signals U In of average level which deliver the applicable data words out of the particular value range of values, both on line 15 from the A/D converter 14, and on line 25 from the A/D converter 26.
- the range of levels of the analog audio signal U In that is suitable for this purpose, also is determined from the relationship sw/2 ⁇ U In ⁇ sw, sw being the above-mentioned threshold value. Only if this condition is satisfied should the coefficient register 14 be actualized.
- an additional Schmitt trigger 76 is connected to the output of the full-wave rectifier 32 and delivers an output signal to a gate 78 when the level of the audio signal U In reaches the value sw/2 and exceeds it.
- the other input of the gate 78 is the inverted output signal from the Schmitt trigger 34.
- the output signal from the AND gate 78 is fed to the gain error detector 44 via line 74 as the activating signal.
- the activation can also be performed by comparing the values x and y within the gain error detector 44.
- the dynamic range of the apparatus is thus expanded by the amount of the chosen amplification factor V.
- the envelope curve generator 68 there are stored two different value ranges, a first one of which is retrieved from the data words entered onto line 63, and the second range is retrieved after a signal is present on line 35.
- the first range of values increases slowly at first as the content of data words arriving on line 63 increases, and then faster, until toward the end of the value range of the data words on line 63 it approaches a limit indicated by the curve shown in the figure.
- the noise signal emitted by the noise generator 72 is multiplied in multiplier 70 by the individual values obtained from the data words on line 63, and the product is fed in adder 74 to the data stream via line 71.
- the second range of values stored in the envelope curve generator 68 increasingly diminishes slope-wise from the above-mentioned upper limit and is retrieved step by step in the sampling cycle through the flank of the control signal present on line 35, which triggers the change over of the switch arm 56 from contact 52 to contact 54.
- a comparison is made of the values with those which are produced simultaneously by the data words on line 63 from the first range of values. The greater of two compared values is fed to the multiplier 70.
- the monostable multivibrator switches back after a preset time period, during which the data stream is taken from the signal path 2 by the switch 5, even though the amplitude of the audio signal that is to be converted would justify its conversion in signal path 1.
- stage 66 it is possible in the manner described to bridge over the abrupt increase of the noise level when switching from one signal path to the other with switch 5, without the need for any delaying of the audio signal or data streams.
Abstract
Description
Claims (13)
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE4420713A DE4420713C2 (en) | 1994-06-14 | 1994-06-14 | Device for converting analog audio signals into a digital data stream |
DE4420713.1 | 1994-06-14 | ||
DE19502047A DE19502047C2 (en) | 1995-01-12 | 1995-01-12 | Process for analog-digital conversion of signals |
DE19502047.2 | 1995-01-12 |
Publications (1)
Publication Number | Publication Date |
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US5600317A true US5600317A (en) | 1997-02-04 |
Family
ID=25937408
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US08/490,136 Expired - Lifetime US5600317A (en) | 1994-06-14 | 1995-06-14 | Apparatus for the conversion of analog audio signals to a digital data stream |
Country Status (3)
Country | Link |
---|---|
US (1) | US5600317A (en) |
EP (1) | EP0707383B1 (en) |
DK (1) | DK0707383T3 (en) |
Cited By (34)
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---|---|---|---|---|
US6195031B1 (en) * | 1998-12-28 | 2001-02-27 | Siemens Aktiengesellschaft | Analog-to-digital converter with level converter and level recognition unit and correction memory |
US6288664B1 (en) | 1999-10-22 | 2001-09-11 | Eric J. Swanson | Autoranging analog to digital conversion circuitry |
US6310518B1 (en) | 1999-10-22 | 2001-10-30 | Eric J. Swanson | Programmable gain preamplifier |
US6414619B1 (en) | 1999-10-22 | 2002-07-02 | Eric J. Swanson | Autoranging analog to digital conversion circuitry |
US6590517B1 (en) | 1999-10-22 | 2003-07-08 | Eric J. Swanson | Analog to digital conversion circuitry including backup conversion circuitry |
US6965658B1 (en) | 1999-10-15 | 2005-11-15 | Telefonaktiebolaget Lm Ericsson (Publ) | Method and means for telecommunication |
US9071268B1 (en) * | 2014-03-05 | 2015-06-30 | Cirrus Logic, Inc. | Multi-path analog front end and analog-to-digital converter for a signal processing system |
US9306588B2 (en) | 2014-04-14 | 2016-04-05 | Cirrus Logic, Inc. | Switchable secondary playback path |
US9337795B2 (en) | 2014-09-09 | 2016-05-10 | Cirrus Logic, Inc. | Systems and methods for gain calibration of an audio signal path |
US9391576B1 (en) | 2013-09-05 | 2016-07-12 | Cirrus Logic, Inc. | Enhancement of dynamic range of audio signal path |
US9467778B2 (en) | 2013-03-15 | 2016-10-11 | Cirrus Logic, Inc. | Beamforming a digital microphone array on a common platform |
US9503027B2 (en) | 2014-10-27 | 2016-11-22 | Cirrus Logic, Inc. | Systems and methods for dynamic range enhancement using an open-loop modulator in parallel with a closed-loop modulator |
GB2539517A (en) * | 2015-06-15 | 2016-12-21 | Cirrus Logic Int Semiconductor Ltd | Systems and methods for reducing artifacts and improving performance of a multi-path analog-to-digital converter |
US9543975B1 (en) | 2015-12-29 | 2017-01-10 | Cirrus Logic, Inc. | Multi-path analog front end and analog-to-digital converter for a signal processing system with low-pass filter between paths |
US9584911B2 (en) | 2015-03-27 | 2017-02-28 | Cirrus Logic, Inc. | Multichip dynamic range enhancement (DRE) audio processing methods and apparatuses |
US9596537B2 (en) | 2014-09-11 | 2017-03-14 | Cirrus Logic, Inc. | Systems and methods for reduction of audio artifacts in an audio system with dynamic range enhancement |
US9654134B2 (en) | 2015-02-16 | 2017-05-16 | Sound Devices Llc | High dynamic range analog-to-digital conversion with selective regression based data repair |
WO2017127618A1 (en) | 2016-01-21 | 2017-07-27 | Cirrus Logic International Semiconductor, Ltd. | Systems and methods for reducing audio artifacts from switching between paths of a multi-path signal processing system |
US9762255B1 (en) | 2016-09-19 | 2017-09-12 | Cirrus Logic, Inc. | Reconfiguring paths in a multiple path analog-to-digital converter |
US9774342B1 (en) | 2014-03-05 | 2017-09-26 | Cirrus Logic, Inc. | Multi-path analog front end and analog-to-digital converter for a signal processing system |
US9780800B1 (en) | 2016-09-19 | 2017-10-03 | Cirrus Logic, Inc. | Matching paths in a multiple path analog-to-digital converter |
US9813814B1 (en) | 2016-08-23 | 2017-11-07 | Cirrus Logic, Inc. | Enhancing dynamic range based on spectral content of signal |
US9831843B1 (en) | 2013-09-05 | 2017-11-28 | Cirrus Logic, Inc. | Opportunistic playback state changes for audio devices |
WO2018031525A1 (en) | 2016-08-10 | 2018-02-15 | Cirrus Logic International Semiconductor, Ltd. | Multi-path digitation based on input signal fidelity and output requirements |
WO2018031646A1 (en) | 2016-08-11 | 2018-02-15 | Cirrus Logic International Semiconductor, Ltd. | Multi-path analog front end with adaptive path |
US9917557B1 (en) | 2017-04-17 | 2018-03-13 | Cirrus Logic, Inc. | Calibration for amplifier with configurable final output stage |
US9929703B1 (en) | 2016-09-27 | 2018-03-27 | Cirrus Logic, Inc. | Amplifier with configurable final output stage |
US9955254B2 (en) | 2015-11-25 | 2018-04-24 | Cirrus Logic, Inc. | Systems and methods for preventing distortion due to supply-based modulation index changes in an audio playback system |
US9967665B2 (en) | 2016-10-05 | 2018-05-08 | Cirrus Logic, Inc. | Adaptation of dynamic range enhancement based on noise floor of signal |
US9998826B2 (en) | 2016-06-28 | 2018-06-12 | Cirrus Logic, Inc. | Optimization of performance and power in audio system |
US10008992B1 (en) | 2017-04-14 | 2018-06-26 | Cirrus Logic, Inc. | Switching in amplifier with configurable final output stage |
WO2019036579A1 (en) | 2017-08-18 | 2019-02-21 | Cirrus Logic International Semiconductor, Ltd. | Multi-path analog system with multi-mode high-pass filter |
US10321230B2 (en) | 2017-04-07 | 2019-06-11 | Cirrus Logic, Inc. | Switching in an audio system with multiple playback paths |
US10785568B2 (en) | 2014-06-26 | 2020-09-22 | Cirrus Logic, Inc. | Reducing audio artifacts in a system for enhancing dynamic range of audio signal path |
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JP3479433B2 (en) * | 1997-07-02 | 2003-12-15 | 理想科学工業株式会社 | Overfeed detector |
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- 1995-06-14 DK DK95250144T patent/DK0707383T3/en active
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US6195031B1 (en) * | 1998-12-28 | 2001-02-27 | Siemens Aktiengesellschaft | Analog-to-digital converter with level converter and level recognition unit and correction memory |
US6965658B1 (en) | 1999-10-15 | 2005-11-15 | Telefonaktiebolaget Lm Ericsson (Publ) | Method and means for telecommunication |
US6288664B1 (en) | 1999-10-22 | 2001-09-11 | Eric J. Swanson | Autoranging analog to digital conversion circuitry |
US6310518B1 (en) | 1999-10-22 | 2001-10-30 | Eric J. Swanson | Programmable gain preamplifier |
US6369740B1 (en) | 1999-10-22 | 2002-04-09 | Eric J. Swanson | Programmable gain preamplifier coupled to an analog to digital converter |
US6414619B1 (en) | 1999-10-22 | 2002-07-02 | Eric J. Swanson | Autoranging analog to digital conversion circuitry |
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US9467777B2 (en) | 2013-03-15 | 2016-10-11 | Cirrus Logic, Inc. | Interface for a digital microphone array |
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US9680488B2 (en) | 2014-04-14 | 2017-06-13 | Cirrus Logic, Inc. | Switchable secondary playback path |
US9306588B2 (en) | 2014-04-14 | 2016-04-05 | Cirrus Logic, Inc. | Switchable secondary playback path |
US10785568B2 (en) | 2014-06-26 | 2020-09-22 | Cirrus Logic, Inc. | Reducing audio artifacts in a system for enhancing dynamic range of audio signal path |
US9337795B2 (en) | 2014-09-09 | 2016-05-10 | Cirrus Logic, Inc. | Systems and methods for gain calibration of an audio signal path |
US9998823B2 (en) | 2014-09-11 | 2018-06-12 | Cirrus Logic, Inc. | Systems and methods for reduction of audio artifacts in an audio system with dynamic range enhancement |
US9596537B2 (en) | 2014-09-11 | 2017-03-14 | Cirrus Logic, Inc. | Systems and methods for reduction of audio artifacts in an audio system with dynamic range enhancement |
US9503027B2 (en) | 2014-10-27 | 2016-11-22 | Cirrus Logic, Inc. | Systems and methods for dynamic range enhancement using an open-loop modulator in parallel with a closed-loop modulator |
US10720888B2 (en) | 2014-10-27 | 2020-07-21 | Cirrus Logic, Inc. | Systems and methods for dynamic range enhancement using an open-loop modulator in parallel with a closed-loop modulator |
US9654134B2 (en) | 2015-02-16 | 2017-05-16 | Sound Devices Llc | High dynamic range analog-to-digital conversion with selective regression based data repair |
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Also Published As
Publication number | Publication date |
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EP0707383B1 (en) | 2002-05-02 |
EP0707383A1 (en) | 1996-04-17 |
DK0707383T3 (en) | 2002-08-19 |
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